Skip to main content

Full text of "THE ATMOSPHERE OF MARS IN THE LANDING AREA OF THE DESCENT APPARATUS OF MARS-6 (PRELIMINARY RESULTS)"

See other formats


NASA TECHNICAL TRANSLATION NASA TTI'F-IS , 717 



THE ATMOSPHERE OF MARS IN THE LANDING AREA 
OF THE DESCENT APPARATUS OF MARS- 6 
(PRELIMINARY RESULTS) 



M. Ya. Marov et al. 



/{raSfl-TT-F-l57T7) THE ATMOSPHEBE OF MAHS ' N74-27 33T^ 

IS THE LAMDING ABEA OF fHE DESCENT 

APPAIATUS OF MAIS -6 (PEELIHINABY EESCJLTS) 

(Kaisner (Leo) Associates) 29 p HC $4.50 Onclas 

( CSCL 03B G3/30 40885 



Translation o£ ij'Atmosfera Marsa v 
Rayone Posadki Spuskayemogo Apparata 'Mars-6' 
CPredvaritel'nyye Rezul ' taty) ," Report, 

Institute of Space Research, Academy of Sciences USSR 
Moscow, 19Jh, 28 pp 




NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D. C. 20546 JUNE 1974 



STANDARD TITLE PAGE 



1- Report No. 

NASA TT F-15,717 



2. Government Accession Np. 



3^ Recipiont's Cafalog ^^o. 



4, Ti,uands„bti,i. ^^g ATMOSPHERE OF MARS IN THI 

^LANDING AREA OF THE DESCENT APPARATUS 01 
MARS-(j (Preliminary Results) 



5. Rsparf DalB 

-TiiTif^ 1Q7 4 



6. PerFerming Organization Coda 



7. Authorfj) M. Ya. Marov et al, 



B. Performing OrgoniiotiDn Repart No. 



10. Work Unit No- 



9. Performing Orgoniiation Noma and Addrsfr-, 

Leo Kanner Associates ^^ 
P. 0. Box 5187 
■ Rf^flwood City. Cal 94506 



11- Contract or Grant No. 

NASw-2^81 



r-- --'0 .. x:i ] 



13. Type of Rsport and Period Covered 

Translation 



12. Sponsoring Agancy NamQ and Addresv 



NASA, Code KSS-1 
Washington, D. C. 



20546 



\i. Sponsoring Agency Code 



IS. Supplementary Kotas Translation of 'OA.tmosfera Marsa v Raj^bne Posadki 
Spuskayemogo Apparata 'Mars- 6 ' (Predvaritel 'nyye Rezul ' taty) ," 

Report , lii&tltutfe.: of Spaee Research, Academy of Sciences USSR, Mosco-w, 
197^, 28 Vp ■ 



16. Abstroct 



17. Key Words (Selected by Auttior($)l 



IS. Distribution Statement 



Unclassified. '^■I -limited 
EASA ONLY 



19, Security Cia»sif. (of Ihti report) 

None 



20. Security Claifif. (of thi« poge) 

None 



21- No. of Paget 

27 



,22. Price ■ 



NASA-HQ 



THE ATMOSPHERE OF MARS IN THE LANDS AREA c-j; T.:,: 
OF THE DESCENT APPARATUS OF MARS -6 
(PRELIMINARY RESULTS) 

V. S. Avduyevskiy, V. I. Alyshin, N. F. Borodin, 
V. V. Kerzhakovich, Ya. V. Malkov, M. Ya. MarovJ 
S. F. Morozov, V. G. Perminov, M. K. Rozhdestvenskiy, 
0. L. Ryabov, M. I. Subbotin, V. M, Suslov, 
Z. P. Cheremukhina and V. I . Shkirina 

On 12 March. 1974, the Mars-6 automatic interplanetary (/V 
station (AIS) , launched 5 August 1973, reached the vicinity o£ 
Mars, and after a final course correction, the descent apparatus 
(DA) was released. The final correction was made automatically 
by means of the on-board astronavigation system. The engine of 
the descent apparatus shifted it into a trajectory terminating 
on the planet's surface. After that, a programmed turn was exe- 
cuted to provide the necessary angle of attack for an entry into 
the atmopshere. The orbital apparatus (OA) , also after perform- 
ing a programmed rotation, continued its flight in a heliocen- 
tric orbit, passing within about 1600 km from the surface of 
Mars. 

The design of the . Mars-;6^DA and its landing system are 
generally similar to the Mars-3 DA described in [1, 2], The 
apparatus was equipped with a\heat-protective aerodynamic cone, 
protecting the DA from the highc;temperatures developed in the 
area of the shock wave in front of the apparatus and slowing it 
from its hypersonic velocity upon entry to the atmosphere to a 
speed of about Mach 3.5, at which time the parachute system 
was activated. The parachute system was a/imultistage system, 
with a pilot chute and a main chute ^ (initially reefed). The on- 
board automatic equipment, in combination with the radio 
altimeter (RA) , a time programming device and acceleration sen- 
sors, generated the necessary commands, including the command to 

*Numbers in the margin indicate pagination in the foreign text. 

+Frincipal investigator 



switch on the soft landing motor.i.and release the parachute. [1_ 
The descent of the DA is diagrammed in Figure 1. 

The program of motion of the DA in the atmosphere consists 
of the following main elements; 

-- when the DA enters the atmosphere, when a longitudinal 
g load of n = -2 is reached, the command is given to start the 
solid fueled motors which stop the rotation of the DA around its 
longitudinal axis; 

-- when a speed of about Mach 3.5 is reached, the command is 
given to release the pilot parachute, followed by the main para- 
chute, reefed to 0.4 (S.^.^^ = 90 m^, C^ = 1.0-1.2); 

after 12 seconds, the main parachute opens, after two 

more seconds the cone is dropped and after 5 seconds the RA is 
turned on; 

-- after a certain time, the soft landing engines are 
extended. 

The total weight of the system carried by the parachute 

Sa " ^^^ ^^* 

Information from the DA during the time of aerodynamic 
braking and descent on the parachute was relayed through the 
Mars-6 OA to Earth. In the immediate vicinity of the surface, 
at a velocity of Vj,. = 60-65 m/sec, radio communidation with the 
descent apparatus was interrupted. The DA reached the surface 
of Mars in the area of Margaritifer Sinus, in a region with 
nominal coordinates of 23.9" S, 19.5° W. 

Combined analysis of the information transmitted by the DA 
indicates that the descent was nominal right up to 0-2 sec 
before touchdown and yields some information. on the parameters 
of the atmosphere of Mars in the region of the descent from the 
surface to an altitude of about 80 km, satisfying all measured 
data. The initial information includes data from measurements 
of the mutual velocity of the OA and DA V„Ct), measurements of 
the g loads n ft), measurements of the atmospheric pressure 



P(t) and altitude above, the surface h(t) . The models produced /3^ 
by measurement were subsequently compared with models used in the 
plan calculations. 

In order to provide a check o£ the motion of the DA and to 
estimate the parameters of the atmosphere on the basis of the 
resultsc of the actual descent of the Mars-6 spacecraft, the 
mutual velocity of the OA and DA was measured. After receipt 
by the OA, amplification and shifting to the low-frequency range, 
the carrier signal from the DA was relayed to Earth over the OA- 
Earth radio link. 

On Earth, the parameters of the relayed signal were contin- 
ually measured, it was recorded on a wide-band analogi.tape ii; 
recorder and, after analog to code conversion, on digital tape 
recorders. The use of highly stable temperature-controlled 
oscillators on the OA and DA allowed the frequency of the relayed 
signal to be used to determine the difference in velocities of 
DA and OA in the projection on the DA-OA line . CFigiirer2) . Here 
Vp.J-.^ is the mutual ray velocity. Due to aging of the crystal 
resonator of the DA during the flight, the mutual velocity was 
determined with an accuracy determined by a constant component. 
The performance of such measurements represented a very complex 
task due to the low signal/noise ratio resulting from the limited 
power of the on-^board transmitters and the very rapid change in 
Doppler frequency as the DA decelerated in the atmopshere. 

The results of measurements of the velocity are shown in 
Figures 3a and b. Measurements of velocity were performed fori'. 
about 25 minutes over the flight sector preceding entry of the DA 
into the atmosphere and for about an additional 200 sec during 
the descent in the atmosphere down to the surface. During this 
stage, the data produced by the trajectory measurement system of 
the Center for Long Range Space Communidations were used. During 
the sector of rapid velocity change (from the moment of restora- 
tionodf communications to 12:08:50), measurements were performed 
using the recording of signal frequency on a visual recording /4 



device. These data are preliminary in nature and relate to a time 
of about ±3 sec (horizontal line on Figure 3). 

As we can see, the preatmospheric section shows a compara- 
tively slow increase in velocity; measurements during this section 
were used to refine the trajectory of the DA. At an altitude of 
68 km, the concentration o£ plasma around the DA exceeded the 
critical value, causing a loss of communication. Communication 
was restored in about 80 seconds, when the spacecraft reached an 
altitude of 21 km. The first derivative of velocity at the 
moment when communication was restored was 45 m/sec . The subse- 
quent measurement sector was characterized by i.a sharp change in 
^Dft^ due to the deceleration of the DA in the atmosphere. The 
section up to 12:08:32 corresponds to braking by the aerodynamic 
cone, vfhile the bend at 12:08:32 (altitude 11.6 km^ corresponds 
to the sudden increase in braking as the parachute system opened. 
The "minimum" in the measurements of mutual velocity at 12:09:04 
corresponds not to an actual minimum in DA velocity, but rather 
the. ..moment when the derivative of the DA velocity in its 
projectionuoni^the DA-OA line becomes equal to the corresponding 
projection of the gravitational acceleration of the OA. During 
its subsequent descent, the DA became quasistationary, and the 
change in velocity was relative slow, since the main portionoof 
the change in mutual velocity resulted from the movement of the 
orbital apparatus. 

The DA-OA sighting line during the quasistable descent 
sector was inclined to the local horizon of the DA at an angle 
of about 35**, while its projection was directed almost along a 
latitude line. Due to this, the zonalXwind component is included 
in the quasistable descent sector with a coefficient of near 
unit (see [3]) . 

The analysis of the Doppler measurements performed at the 
time, inccomparison to the DA descent version calculated before 
the landing showed that: 

-- the DATentered the atmosphere at a moment near the time 



calculated for an entry angle of about 11.5°; 

-- the parachute system functioned normally (the bend on 
the velocity curve at 12:08:32 corresponds to the release of the 
parachute, while the lack of variations in velocity indicates 
a smooth descent through the atmosphere) ; 

-- the time of descent of the spacecraft on the parachute for 
an entry angle of about 11.5° corresponds to an atmosphere with 
a surface pressure:;of about 6 mbar. 

The Doppler measurement data were used to determine also 
the variations In ray velocity of the DA in the quasistable 
descent sector. Noticeable variations with amplitudes of 2-4 
m/sec and periods of 10-20 sec were observed up to about 12:09:50 
and were apparently; a result of oscillations in the parachute-DA 
system following perturbation upon entry and ^unreefing of the 
parachute and at the moment of release. Subsequently, oscilla- 
tions with amplitudes of over 2 m/sec were not observed, and the 
course of thejimeasurement curve of velocity remained near the 
calculated course. This indicates, first of all, a smooth space- 
craft descent without strong swinging (although we should recall 
that only one velocity component was measured) and, secondly, 
slight variation in wind speed, including the vertical component 
(time constant of parachute-DA system is about 15 sec). The near 
nominal nature of the change in mutual velocity also indicates 
a slight (less than 5-7 m/sec) change in wind speed at altitudes 
of to 7.5 km. 

The axial g loads were measured during the preparachute 
aerodynamic braking sector in the atmosphere of Mars in order to 
determine the density of the atmosphere and trace the dynamics of 
motion of the apparatus. The change in g load as a function of 
time n (t) is shown in Figure 4. 

The g load measurement system consisted of an inertial 
sensor with a potentiometer and flip-flop memory registers. The 
system performs the following logic functions: 

-- recording of moments of attainment of preselected ,K.r.ciD:i. 



acceleration levels; / /6 

-- determination o£ the maximum value of g loads and cor- 
responding moments in time; 

-- storage of information until the beginning of operation 
of the DA telemetry system. 

Considering the systematic temperature and random errors 
of the sensor, the values of axial g loads for which times were 
recorded were as follows : 

--on the ascending branch, 4.2 ± 0.25 and 9.75 ± 0.2 5 

t^x2' ^x3^ 

-- on the descending branch, 4.2 + 0.25 (n . ) . 

The summary error in measurement of the maximum g load is 
±1.2% of the rangei;of measurement, corresponding to ±0,45 accel- 
eration units, and including the methodological error (±1^) and 
the error of the sensor (0.7%). 

The measured value of maximum axial acceleration was n^ ^^^ = 
+n 4d max 

= 9.8 „*_ . The lower boundary was determined by the previous 

level of accelerationuonuthe ascending branch 9.75 ± 0.25. The 
time to fixed levels of acceleration and to the moment of achieve- 
ment of its maximum value were calculated from the level n , = 

+ 25 ^ 

= 2_!^' .on the ascending branch of the curve (Figure 4). With a 

smooth maximum on the curve of axial .acceleration, the time of 

achivement of n^ ^^^ corresponds to the left boundary of the 

interval in which the maximum value is reached. The measured 

integral times were: 

-- in the ascending branch t -t =9.2±0.25 sec and 

^x2 ^xl 
t - t = 23.8 ± 0.25 sec; 
^x3 ■ "xl 

--in the descending branch t ~ t =57.2+0.5 sec; 

'^x4 ^xl 
--to the maximum acceleration t - t = (2 8.6 ± 0.5) 

X max xl 
sec. 

The value of maximum axial acceleration found can be used 

first of all to determine the level n = (0.14 + 0.01) n 

^5 ^max 



= 1.37 ±0.15, used to actuate the parachute system of the DA. /7 
On Figure 4, the solid line shows the design dependence o£ accel- 
eration on time for the conditions of entry of the DA of the 
Mars-6 spacecraft and the model of the atmsophere of Mars with 
surface parameters P„ = 5 mb, T^. = 200 K with a tropopause alti- 
tude h. = 12 km. The level of n -, = 2 was also used as the 
t xl 

beginning of the reading. As we can see, the difference between 
measured and calculated values for the limiting measurement 
errors in this case falls within limits of one sec. 

To correlate the results produced to the instantaneous time, 
the moment of interruption of radio communication at the surface 
of Mars was used. The processing performed to date yields an 
estimate of this moment of 12:11:05 Moscow time (Figure 3). Since 
the duration of transmission of telemetry information during 
the parachute section was 149.2 sec, the time of operation of the 
parachute system of the DA 2.4 sec and the time of selection of 
n r 1.5 seCf we can estimate. the passage through g load level 
n r on the descending branch of the curve as 12:08:32, which 
agrees well with the break point on the curve of V^(t) (Figure 3). 
The characteristics of the Martian stratosphere were estimated 
using a method presented in [4] . On the assumption of an iso- 
thermal stratosphere over the measurement section, the temperature 
range T = 120-190 K was studied, with a corresponding logarithmic 
density grandient e = 0.1-0.165 km . At the lower boundaryoof 

the isothermal layer h , the density was assumed to be p, 

f 
- 3 3 

= (4- 7) '10 kg/m . As a result of solution of the system of 

equations of motion of the DA in the atmosphere, values of time 
intervals and maximum acceleration were calculated within the 
fixed range of temperature of the stratosphere (Figure 5a, b) , as 
well as the intervals of time from the entry into the atmosphere 
to the level n ,. = 2 and from the level n . to n ^ on the 
descending branch of the curve (Figure 5c) . The results of /8_ 
calculations were compared with the measured values of these 
quantities. in the overlapping ranges of parameters . commonii too 



+ 8 
all measurements, the mean stratosphere temperature T = 144_g K 

and respectively g = 0.137*? qq^ km" . The nominal values of 

measured parameters on the ascending branch (Figure 5a, b, dotted 

line) correspond to T = 152*g K and B = 0.130^^-^^^ km"-*", on the 

descending branch T = ISS^g K and = -"-^^^oooe ^™'-^- '^^^ ^^^~ 
perature T = 144^? K corresponds to p, = (5.1 ± 0.4- lO" km) 
(Figure 6a, b) . In the altitude area S > h , the density is deter- 
mined £rom\.:thei;exponential dependence p = p, e -^ij( t. 

The mean temperature T = 144 K (Figure 5a, b) corresponds 
to. the following values of measured quantities: 

--in the ascending branch At = 8.95 sec and n =4.45; 
At = 23.55 sec and n = 9.75; 

-- on the descending branch At - SI .7 sec and n = 9.75; 

-- n = 10.2; At = 28.4 sec. 
X max ' ' n „„, 

X max 

If we utilize the model of the atmosphere presented above above 

the h. level, then, as follows from Figure 6c in the range of 

altitudes where axial g loads were measured, h ^ .. .+3 , 

x2 ■ ' 

h = IS.e'-'^-^km; h = 23'*'?;o,km. 
^x4 N max '^'^ ' 

^ Restoration of the picture of motion during the deceleration 
sector allows us to refine the ballistic prediction of the time of 
arrival of the DA at the arbitrary upper boundary of the atmos- 
phere of Mars and determine the duration of the preparachute 
descent sector. Calculations show that the entry angle of 12° 09' 
(ballistic prediction) is near the actual angle. With angles of 
less than 11.5" or more than 12.5", the measured and calculated 
time intervals for passage through the various values of n dis- 
agree, which is difficult to correlate with the usual assumed 
parameters of the stratosphere of Mars. However, we should note 
that the isoterhaml distribution of temperature in the strato- 
sphere corresponds to the limiting values of measured time /_9 
intervals and accelerations. Therefore, we can assume that the 
profile of temperature in this area differs somewhat from iso- 
thermal, with temperature gradients in some sectors determined 

8 



by the limiting values of the approximating;^ isotherms T = 138_^ K 
and 152^g K. 

To allow direct determination o£ the parameters of the atmos- 
phere, the/ Mars-6 DA carried devices for measurement of its 
temperature andJ.pressure and a mass spectrometer. Results of analy- 
sis of the telemetry information concerning the operation of the 
mass spectrometer are reported by Istomin et al. [5]. The P and T 
sensors were membrane manometers and resistance thermometers/, . 
The sensing element of the resistance thermometers was a platinum 
wire 50 mm in diameter with bifilar winding in the form of a rec- 
tangular frame. The frame was suspended on strips of mylar film 
to a pressboard frame. 

The range of temperatures measured during the descent sector 
was from -150 to +50° C, with .a standard (mean square) terror 
of measurement of ±5^ of full scale [{according to laboratory 
calibration under conditions similar to those encountered) . 

The pressure sensor, designed for a measurement range of 
to 12 mbar with a standard (mean square) measurement error of 
±5% of the full scale in the temperature range from --20 to +50° 
e utilized a metal membrane 1.8 cm in diameter and 100 y thick and 
a capacitive sensing element. The working volume of the sensor 
was evacuated on the DA side. The possible uncontrolled zero 
drift was not over 1 mbar. 

The pressure and temperature sensors were designed primarily 
to perform measurements on the surface of Mars; therefore, they 
were not to be exposed Until after the landing and adjustment of 
the DA to its operating state. Measurements using some of the /lO 
parachute descent sector were supplementary in nature. This con- 
cerns primarily the temperature, since direct measurement in a 
stream of rarefied gas, considering the possible influence of 
hot streams from the boundary layer and irradiation of elements 
of the spacecraft structure heated. during the aerodynamic braking 
sector, might be significantly in error, and correction is quite 
difficult. The data from temperature measurements can be 



further analyzed considering modeling results. 

The results of measurements of pressure and altitude over 
the surface in the area of descent of the spacecraft as a func- 
tion of time are shown in Figure 7. Since the P sensor was 
carried in the tail portion of the spacecraft, the measurement 
data were corrected to consider the difference of the full head 
from the static pressure using the dependence 

P = P (1 + ^-^ M^}"^/^'^ 
meas ^ 2 -^ , 

where K = C /C is the ratio of heat capacities at constant 

IT *' 

pressure and constant volume for CO^; 

M is the Mach number (M < 1 over the entire measurement 
sector). The vertical . lines indicate the measurement errors, the 
arrow along the ordinate shows the possible zero drift, which 
might cause an increase in the total [random plus systematic) 
error of measurement to approximately double its value) Approx- 
imation by a second-power polynomial quite satisfactorily des- 
cribes the initial fields of measured points P(t) and h(t). At 
the end of the measurement at the surface of the planet in the 
area./where the apparatus landed, the pressure was P = 6.1 ± 0.5 
mbar. 

Figure 8a shows the change in pressure during the time of 
parachute descent as a function of altitude. Here also we show 
the logarithmic pressure gradient and an estimate of the tem- 
perature of the atmosphere, produced using the obvious relation- 
1-- d In P 1 ,,1,^^^ u - RT ^ 

In this (isothermal here H = const) approximation, the mean 
temperature of the troposphere of Mars is 228 + 10 K. Consider- 
ing the errors in determination of P, an attempt to produce the 
dependence TCh) in the approximation H ^ const is hardly justi- 
fied. Figure 8b shows the dependence of changes of density on 
altitude, calculated on the basis of the hydrostatic equation 
and the equation of a quasi-even descent on the parachute for 

10 



various values o£ C . The best agreement with the calculated 
values using the equation for hydrostatic equillibrium for mea- 
sured values of P(h) occurs for C =0.95. 

In additiont'to (the separate analysis of measurements, Lthe 
results of which are presented above, an attempt was made at 
combined utilization o£ the measurements o£ V^Ct) , h(t) , PCt) and 
n^(t} for most reliable determination of the parameters of the 
Martian atmosphere. Performance of this task is a very difficult 
problem, involving a large number of influencing factors, related 
not only to the atmosphere itself, but also to inaccuracies in 
determination of the aerodynamic characteristics of the apparatus 
with its:;,complex functioning plan, inaccuracies in determination 
of the trajectory of the DA and OA, etc. The task was performed 
by multistage variation of parameters of the atmosphere, as well 
as variation of the flight trajectory of the DA until all the 
measurements were satisfied. 

It was. assumed that the atmosphere of Mars consists of two 
sections -- the convective section with linear change in tempera- 
ture with ..jgradieht/.^YJ .:.and.'- an isothermal section beginning at 
latitutde h. . The altitude was related to the level with pressure 
6.1 mb, which.;.attthe latitude of the landing point (-23.9° S) 
according to radio occultation '.studies [6], corresponds to a 
distance of 3392 km from the center of Mars. The variable para- 
meters of the atmosphere were: temperature near the surface T^,, 
height of tropopause h^, temperature gradient y* which auto;- 
matically led to variations in the temperature of the isothermal 
section TT ;.:..=?. T„ - yh^. The primary variable parameter in the 
trajectory used was the normal component of velocity of the DA at 
the moment when the spacecraft received its braking impulse (a 
distance of about 45000. .;km from the center of Mars) , It was this 
component which, through variation of the angle of entry, had the 
greatest influence on the movement of the DA. During integration 
of the equationstjof i'lhoition, the compression of the gravitational 
field of Mars [7] and combustion of the aerodynamic cone were c.<i:..- 



11 



considered; it was further assumed that, i.alL amotion occurred at 
angle o£ attack, the atmosphere consists of pure CO2 , and the 
windspeed throughout the entire descent was assumed equal to 0. 

The solution had as its task the production of agreement 

between calculated curves for PCt), ^^^^^ ' ^^^^ ^^^ ^D^^-* ^^'^^ 
measured curves, adjusted to current time. It should be noted 
that the dynamic and trajectory parameters were sensitive to 
density; therefore, estimates of temperature distribution on 
their basis can be performed only with limited accuracy. 

As a result of the calculations performed, it was found that 
at the current stage of analysis, the entire set of measurements 
availableis best satisfied by an atmosphere with the following 
parameters: Tq = 230 K; T^ = 155K, y = 2.S°/km, h^ w 30 km, 
meaning that the pointi of contact with the surface lies at an 
altitude of 400 m above the relative level P = 6.1 mb, so that 
the calculated pressure at the surface is P^ = 5.9 mb. The 
vertical velocity of the apparatus at the surface was 61 m/sec. 
The results of calculation are presented in Figure 9. Along 
with the. calculated values, we show the measured dependences of 
P(t), hCt) , Vp,Ct) and n (t) for this model. The difference between 
the calculated altitude and the measured altitude (in addition to 
the systematic deviation of about 400 m, related to the local 
relief) over the entire section is 50- 100m, the deviation of 
pressure Ap < 0.2 mbar, of acceleration An < 0.4 g, of velocity 
aV^, < -7 m/sec. The calculated time of operation of the para- 
chute system and loss of signal upon entry into the atmpsphere 
coincide to the measured values with an accuracy of about 3 sec. 
The calculated, somewhat lower values of acceleration, in addi- 
tion to measurement errors, may be explained by a slightly lower 
temperature (about 145 K) of the stratosphere, as was indicated by 
separate analysis of the measurement data of n (t) . 

At present, it^i's di£ficult;:to make an estimate of the accuracy 
of determination of the parameters of lithe atmosphere corresponding 
to Ithe model presented in Figure 10. Analysis of various versions 



12 



shows that the accuracy of estimation o£ temperature at the sur- 
face is ATf, == ±20 K, of^^pressure ±0.5 mb, of temperature above 
the level o£ the tropopause aT^ - ±10 K, of windspeed aV = ±10 m/ 
sec. 

The data of remote measurements of the parameters of the 
atmosphere by the Mariner-4, 6, 7, 9 and Mars 2-7 spacecraft 
generally agree well with the direct measurements presented and 
the estimates produced by analysis of the descent. The data o£ 
measurements of Mars -5 in a region adjacent to the area of landing 
of Mars-6 show that the atmospheric pressure, determined by absorp- 
tion in the bands of CO2 is 5-6 mbar [8]. For comparison, Figure 
10 also shows the altitude profiles of atmospheric parameters 
according to the working models of, the atmosphere of Mars [9, 10]. 

The results of combined analysis also yield certain pre- 
liminary estimates on the dynamics of the Martian atmosphere. 
The agreement of calculated and measured values of the mutual 
velocity shows that over the last 100 sec of descent, i.e., at 
0-7.5 km altitude, the windspeed was apparently near 0. 

We note here that a variation in atmosphere parameters (as 
well as OA trajectory parameters) leads to near parallel shifts 
in mutual velocity over the section of quasistable descent. 
Therefore, agreement between calculated and measured quantities /14 
could also be attained with other atmospheric parameters, by intro- 
ducing a wind with a velocity near constant with changing altitude. 

However, considering the good agreement of calculated and 
measured (by radio altimeter) . descent rates, it is imporbable 
that the value of the constant component of windspeed exceeded 
about. 10 m/sec, or that the change of wind with altitude was 
over 5-7 m/sec. 

The results of analysis of the descent of the Mars-6 APS 
descent apparatus in the atmosphere of Mars are preliminary in 
nature . and require further refinement. 



13 



The authors would like to take this opportunity to express 
their deep gratitude to their many colleagues who participated 
in the preparation and performance of this difficult experiment, 



14 



REFERENCES 



1. Pravda, No 353(19496), 19 December 1971. 

2. Marov, M. Ya. , G. I. Petrov, "Investigations of Mars from the 
Automatic Stations Mars 2 and 5," Icarus 19 , pp. 163-179, 1973. 

3. Kerzhanovich, V. V., M. Ya. Marov, M. K. Rozhdestvenskiy , 
"Data on Dynamics of the Subcloud Venus Atmosphere from Venera 
Spaceprobe Measurements," Icarus il7 . No. 3, pp. 659-674, 1972. 

4. Cheremukhina, Z. P., S. F. Morozov, N. F. Borodin, "Estima- 
tion of the Temperature of the Stratosphere o£ Venus by Means 
of Data on g Loads on the Venera 8 Automatic Spacecraft," 
Kosmicheskiye Issledovaniya , Vol. 12, No. 2, 1974. 

5. Istomm, V. G. , et al., Report Presented at Soviet-American 
Meeting , Moscow, 4-8 June 1974. 

6. Cain, D. L. , A. J. Kliore, B. L. Seidel, M. J. Sykes, "The 
Shape of Mars from the Mariner 9 Radio Occultation Measurements,' 
Icarus, 17, No. 2, pp. 517-524, 1972. 

7. Lorell et al, Icarus 18, No. 2, 1973. 

8. Ksanforaaliti, L. V., B. S. Kunashev, V. I. Moroz, '■ Mars^S: 
Pressure and Altitude According to Intensity of CO^ Bands ,' 
Report . presented at Soviet-American Meeting, Mosccft, 4-8 June 
1974. 

9. 'A Working Model of the Atmosphere and Surface of Mars," IKI 
Academy of Sciences USSR , 1971. 

10. Mars Engineering Model ," Viking 75 Project, NASA M7S-125-2, 
1972, 



15 






Figure 1. Diagram o£ Descent o£ DA in Atmosphere of Mars, 
1, Separation o£ DA; 2, Firing of DA Engine; 3, Aerodynamic 
Braking; 4, Parachute Descent [5 not given -- tr.] 



16 




Figure 2 . „,„ oTlSasure^ent of Mutuaf TelodTy "of 



DA and OA 



17 



00 



Figure 3. a and b, JChange in Mutual Velocity of Descent 
Apparatus Vj^ -^c^^Dependenee^^oi^^ 





12,0 aoo CJ.0O 



laOO ILGC -t '_X^Tne 



19 



tSJ 

o 




Figure 4. Change in Acceleration ri as a Function o£ Time 



culation 6£ Time Intervals to Moments 
or Attainment of Fixed Accielerations in Comparison with 
Measurement Data 



"N- 







21 




1 w-t 





22 



• Figure 6. Esti mates of Level of n and Density p, for Meai 

' A^tttn^E^^''^ Temperature T = 144 'K"7irbn^IlTinm^io"n" of"^ 

^^H^Y^^ °^^^ Surface with Corresponding Values of n Cfnr- K-- 

j Millibar Model of Atmosphere), (c) vaiues ot n^ Uor 5-. 




Pressure of Atmosphere of Mars as a Function of Time 







^l' 3)'--r-fJ^^'''--''^"'^^^^va 









,<? 






r-223K 




on 



Pur.R. 



CL _^ 



Figure 8, pa, Change iii Pressure and Pressure Gradient in 
Atmosphere of Mars with Altitude. Estimate of Mean Temperature 
o£ Atmosphere o 



24 



ho 



n,KM 



2w2 




0.0i2 P&2/Ai) 



Figure 8. b. Change in^^^lculated Density with Altitude. 



ON 




Comparison of calculations based 
. on model of Martian atmosphere 
produced with direct measurements J 



i!^easured 'ja '^i 



Figure 9. Combined Analysis o£ Calculated and Measured Values 
for Descent Sector of Mars=6 Spacecraft, 



sm^-ttrnmnmmmii 






MiiTureiLt Ttl\utlnTrefclnt sf ^"^ Satisfying Combined 
Comparison with oihJr Mod" f """ °* **""-« Spacecraft in 



Model of atmosphere o£ Mars in 
the area of landing of Mars -6 DA 



I Exp erimental 

Viking- 7S 
IKI 




IVO 180 ■ ISO 200 2X0 
100 200 500 800 1000 



.20 



j300 I £00 



^^^^^mnmmmm